The present invention relates to a hermetic compressor for small refrigeration appliances, and more specifically to a new constructive solution for the discharge system of a hermetic compressor such as rotary rolling piston type compressor.
The construction of the discharge system in hermetic compressors, especially on rotary rolling piston ones, has an immediate influence on energy and volumetric losses of the compressor.
One of these is the energy loss by over-pressure which has to do with the opening readiness of the discharge valve after the pressure in the cylinder compression chamber has reached the discharge pressure and also, the inadequate efficiency of the discharge system to evacuate the gas to be discharged, as promptly as possible, once the valve is open. In situations which the discharge valve will not open appropriately, the over pressure condition inside of the cylinder compression chamber will occur and, the greater the part of the compression cycle, the greater will be the effort and the energy loss which the compressor crankshaft will have to overcome.
Another type of loss is due to the energy and volumetric losses in terms of existence of the dead volume in the discharge orifice of the compression chamber. What occurs is that the dead volume of the gas left in the discharge orifice returns after each compression cycle to the cylinder, taking up the space of the gas to be accepted at every new suction cycle, causing a relevant volumetric loss. Besides that, the gas that occupies the dead volume in the discharge orifice will be compressed at every compression cycle but will not be discharged from the cylinder, causing the discharge energy in this compression to be wasted, becoming an energy loss of the compressor.
In view of the above, it can be stated that the judicious definition of the construction characteristics of the discharge system is an important part of the dimensioning of a hermetic compressor.
The most conventionally adopted solution for the discharge system of hermetic compressors, especially those of rotary rolling piston type, is the provision of a reed valve with its bumper fastened through screws or rivets to the same plate on which the discharge orifice is arranged.
Another solution for discharge system of the prior art compressors is the use of a cylindrical reed valve, in which a spring steel blade of cylindrical shape is disposed in the interior of the cylinder body, transversely to the discharge orifice, as proposed by U.S. Pat. No. 4,537,567.
Both the reed valve and cylindrical reed valve present operational and construction inconveniences which end up causing energy and volumetric losses in the compressor.
These well-known valves present fastening through their shaft which is fastened to the holding screw or rivet. This construction arrangement provides an inevitable restriction to the discharge free flow.
Besides the above inconvenience, the known valves are open in an inclined way (non-parallel) to the seat, which brings an asymmetry to the discharge flow, making it difficult.
The above operational and constructive characteristics commented upon using reed valves and cylindrical reed valves impair the gas discharge flow of the cylinder compression chamber, increasing the energy loss by over-pressure.
Besides the above problem, the reed valve also presents the disadvantage of needing a quite large seat area which requires a greater thickness of the cylinder body plate on which is provided the seat and the discharge orifice, so that this plate has sufficient mechanical resistance to support the gas compression efforts without deflecting.
In this way, the greater thickness of the already mentioned plate or cylinder wall gives rise to an increase of the discharge orifice length machined in said plate, which, in turn, increases the dead volume of gas in the interior of this discharge orifice with all disadvantages mentioned above.
In spite of minimizing the problem of dead volume at the compression chamber outlet, the cylindrical reed valve requires the provision of a plurality of passages often in parallel to each other and disposed on the cylinder wall, transversely to the discharge orifice and, radially regarding the valve cylindrical blade, so as to interconnect the mentioned discharge orifice with the valve body interior. This type of building structure is difficult to make. Another serious deficiency of both solutions relates to the difficulty of manufacturing the seats. Reed valve seats require a large surface and a complex geometry. On the other hand, the cylindrical reed valve presents a simple geometry but, the building structure is of difficult execution as mentioned above.